0000000001062814
AUTHOR
A. M. Siddiolo
Wooden panel paintings investigation: An air-coupled ultrasonic imaging approach
In this paper, a method for the study of wooden panel paintings using air-coupled acoustical imaging is presented. In order to evaluate the advantages of the technique, several samples were made to mimic panel paintings along with their typical defects. These specimens were tested by means of both single-sided and through-transmission techniques using planar transducers. Image data were processed by means of a two-dimensional (2-D)-fast Fourier transform-based algorithm to increase the S/N ratio and 2-D representations (C-scans) were generated. The simulated defects were imaged using both configurations. Investigations were undertaken on four antique paintings from a private collection. The…
A Direction/Orientation-Based Method for Shape Measurement by Shadow MoirÉ
In this paper, a methodology to process fringe patterns is presented. The core of the signal processing technique is the use of the direction information, which is a modulo quantity that locally indicates the direction along which fringes grow at a maximum rate. By using this information, it was possible to perform adaptive and direction/orientation-based operations on fringe images to remove unwanted effects (mainly distortions at the image borders), to enhance the contrast, and to extract the phase information encoded. The method has been applied on shadow-moire interferograms with carrier fringes in order to measure the surface of small objects. The developed algorithm allows processing …
Thermoelastic Stress Analysis by Means of a Standard Thermocamera and a 2D-Fft Based Lock-In Technique
The thermoelastic effect in a generic orthotropic body under adiabatic and linear elastic stress conditions induces small and reversible temperature changes that can be correlated with the stress field by means of linear relationships. Infrared techniques are mainly used to measure temperature changes on the component surface [1], while adiabatic conditions are generally achieved by applying cyclic loads above a threshold frequency. The resolution resulting from implementing a Thermoelastic Stress Analysis (TSA) technique is a combination of the infrared acquiring system resolution and of the signal post-processing procedure. State of the art infrared detectors have NETD (Noise Equivalent T…
Air-Coupled Imaging Method Applied to the Study and Conservation of Paintings
An air-coupled acoustical imaging method for the study of wooden panel paintings is presented. After a brief overview of the state of the art, an introduction is given regarding the production technique of the art object under investigation. The technology employed is described in detail, as well as the proposed method. After a feasibility campaign of experiments, real ancient paintings have been investigated by means of a through-transmission and a single-sided lay-out. Defects were imaged in all the objects examined and in both the configurations adopted
Wooden Surface Investigation: an Optical Approach Based on Shadow Moiré
The interest in the mechanical behaviour of wood is a very important task due to the increasing role played by wood structures in modern architecture as well as its applicability in restoration of ancient buildings. The behaviour of wooden surfaces experiencing variable humidity conditions is of great importance both with concern to performances of wooden building’s structures and to ensure correct restoration and conservation of art works like wooden sculptures and panel paintings [1]. In literature there are only a few studies dealing with the influence of moisture on the physical properties of wood [1,2]. The characterization of wooden behaviour related to changes in the humidity level c…
A Hybrid Frequency-Space Approach for Shape Measurement by Shadow Moiré Technique with Carrier Fringe Pattern
In this paper, a novel methodology to process fringe pattern is presented. The core of the signal processing technique is the use of the direction information, a modulo 2pi quantity that locally informs about the direction along which fringes grow with maximum rate. By using this information, it was possible to perform adaptive, direction- and orientation-based operations on fringe images in order to remove unwanted effects, to enhance the contrast and to extract the phase information encoded. The method has been applied on shadow moire interferograms with carrier fringes in order to measure the surface of small objects. The developed algorithm allows to process fringes whose phase informat…
Thermoelastic stress analysis by means of an infrared scanner and a two-dimensional fast Fourier transform-based lock-in technique
An infrared thermographic experimental set-up has been proposed and evaluated towards the capability to measure thermoelastic-effect-induced temperature changes. A standard infrared thermocamera with a nominal noise-equivalent temperature difference (NETD) resolution of 0.12 K has been employed to measure the temperature from unidirectional glass-reinforced plastic tensile coupons under cyclic sinusoidal loads. The raster scanning mode of the camera single detector produces a time delay in acquiring the signal from two succeeding pixels on the same row, and from consecutive scanned rows. By exploiting the acquired dwell times, it was possible to produce a periodic pattern on the thermal ma…
Thermoelastic signal processing using an FFT lock-in based algorithm on extended sampled data
A fast infrared scanner is used to acquire the thermoelastic effect induced temperature changes along a line on the surface of cyclically loaded tensile samples. The raster scanning movement of the single detector allows the sampling of temperature versus time. This data are then post-processed by means of a lock-in algorithm coupled with 1D and 2D FFT analyses in order to filter out the thermoelastic signal from the noisy measured signal. A data extension algorithm is proposed which uses the information from different acquired frames to extend the data sampling window. The whole signal processing setup is evaluated on experimental data with successful results, proposing a potential tool fo…
Review of Advanced Acoustical Imaging Techniques for Nondestructive Evaluation of Art Objects
Proper preventative diagnosis of different art objects, including wooden, bronze and marble sculptures, frescoes, and paintings (on canvas, wood, metal, and glass), is very important for conservation purposes. Various advanced ultrasonic imaging methods for analysis and assessment of art objects can bring about drastic changes in the regular evaluation and inventory carried out by museums and can bring advanced, powerful, and new techniques for objective assessment of physical conditions of museum resplendence. Using these methods, it will be possible to plan ad hoc repair works on art objects, and, as a result, we will preserve our heritage. The goal of this review is to introduce recent a…